Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session C07: Focus Session: Advances in Magnetic Resonance Velocity and the 2019 MRV Challenge I |
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Chair: John Eaton Room: 211 |
Sunday, November 24, 2019 8:00AM - 8:13AM |
C07.00001: Advances in Magnetic Resonance Velocimetry and the 2019 MRV Challenge Invited Speaker: John Eaton Magnetic resonance imaging is a leading technique to measure velocity fields in geometrically complex flows. Two recent examples include three-component, phase-locked measurements within rotating turbomachines and 3D velocity field measurements throughout model urban canopies. Advances in scanner hardware, pulse sequences, and post-processing techniques are providing improvements in spatial and temporal resolution with reductions in total scan time and measurement uncertainty. However, there are no agreed upon best practices for measuring mean velocity fields in turbulent flows. The 2019 MRV Challenge addresses this issue. Multiple groups are measuring the velocity field in a specific flow configuration consisting of a square cross section U-bend operated at a Reynolds number of 15,000. This configuration produces strong mean velocity profile distortion and pressure-driven secondary flows posing a significant challenge to any measurement technique. The entire apparatus including the flow development section and the U-bend is shipped from lab-to-lab insuring uniformity of test conditions. The specific measurement techniques used by various groups and a comparison of the data sets will be presented in this focus session. [Preview Abstract] |
Sunday, November 24, 2019 8:13AM - 8:26AM |
C07.00002: The 2019 MRV Challenge Experiment at Stanford University Christopher J. Elkins, Andrew J. Banko, John K. Eaton, Michael J. Benson Specific measurement techniques and Magnetic Resonance Velocimetry (MRV) results for the 2019 MRV Challenge experiment at Stanford University will be presented in detail. Some basic physics behind MRV as well as a general description of how pulse sequences (series of radio frequency pulses and applied magnetic field gradients) are used to make velocity measurements will be introduced. This will provide context for the motivation behind the challenge and the differences observed among the measurements by the participating labs since each lab uses a different pulse sequence in a different MRI system. Specific to the Stanford experiment, the equipment used and the overall setup of the square cross-section U-bend channel in the 3T magnet at the Richard M. Lucas Center for MRI at Stanford will be described. In addition, the parameters of the MRV pulse sequence and post processing steps of the data will be explained. Finally, an overview of the results and uncertainties will be given along with a discussion of the sources of these uncertainties. [Preview Abstract] |
Sunday, November 24, 2019 8:26AM - 8:39AM |
C07.00003: 2019 MRV Challenge: Hanyang University and Korea Basic Science Institute Results. Simon Song, Muhammad Hafidz Ariffudin, Don-Gwan An, Chaehyuk Im, Sukhoon Oh This presentation is part of the 2019 MRV Challenge, and represents the results of a combined team from Hanyang Univ. and KBSI. Four MRI research groups are supposed to make measurements in the same apparatus comprising a square cross section U-bend with a tight radius that will produce a highly three-dimensional flow field with turbulent flow separation. An inlet boundary layer trip marks the common coordinate origin of the flow in the channel. The apparatus being transferred between the research labs includes detailed flow conditioning to ensure that variations in supply and exit plumbing will not disrupt the test section flow. The test was conducted at a turbulent Reynolds number of 15,000 based on the hydraulic diameter. The presentation will focus on the methodology used including the MRI hardware and facility, coil selection, magnetic field strength, scan parameters like number of scans and individual scan duration, software sequence details, as well as post-processing and filtering techniques. In addition, details of the flow at several locations will be presented, along with estimates of uncertainty for each velocity component. Finally, an estimate of experimental effort -- comprised of number of personnel involved and hours, costs, and other factors will be provided. [Preview Abstract] |
Sunday, November 24, 2019 8:39AM - 8:52AM |
C07.00004: Magnetic Resonance Velocimetry in High-Speed Turbulent Flows - Sources of Measurement Errors and a New Approach for Higher Accuracy Martin Bruschewski, Kristine John, Sven Grundmann Magnetic Resonance Velocimetry (MRV) has great potential to become a versatile velocity measurement technique for applied fluid mechanics. One of the most dominant errors in MRV is the effect of displacement which describes the spatial misregistration of the acquired signal in a moving fluid. The overall aim of this study is to highlight the significance of displacement errors in conventional MRV and to provide an improved method. A new MRV sequence, named SYNC SPI (single point imaging with synchronized encoding) has been developed to significantly reduce this error. Measurements were performed in several test cases including a U-bend as part of the 2019 MRV Challenge. In comparison to conventional MRV, this sequence provides reliable velocity data for a wide range of flow velocities. It is shown that flow velocities up to 15 m/s can be accurately measured with this technique. The main disadvantage of the SYNC SPI sequence is the relatively long acquisition time. This disadvantage is partly resolved using a modern undersampling technique called Compressed Sensing to reduce the number of samples required to provide fully-resolved velocity data. It is shown that the acquisition time can be reduced by more than 70\% while still maintaining high measurement accuracy. [Preview Abstract] |
Sunday, November 24, 2019 8:52AM - 9:05AM |
C07.00005: 2019 MRV Challenge: Mayo Clinic Results Daniel Borup This presentation is part of the 2019 MRV Challenge focus session. The results presented were obtained on a Philips 3T Elition X scanner. The flow geometry consisted of a U-bend with square cross section. The flow was fully turbulent with a bulk Reynolds number of 15,000. The flow loop was assembled and operated as described in the MRV Challenge instructions. This presentation will focus on details of the measurement including the hardware, acquisition, and reconstruction method. Particular attention will be given to the choice of scan parameters and pulse sequence used to obtain data. The results from standard 3D Cartesian-trajectory imaging will be presented as a baseline, while data obtained in a shorter time using a ``spiral readout'' trajectory will be shown for comparison. Time-series data in 2D planes in the bend will also be presented to highlight any observations regarding the flow unsteadiness. The measurement uncertainties will also be presented. [Preview Abstract] |
Sunday, November 24, 2019 9:05AM - 9:18AM |
C07.00006: 2019 MRV Challenge: Results and Comparisons Michael Benson, Christopher Elkins, Andrew Banko, Simon Song, Sven Grundmann, Martin Bruschewski, Daniel Borup This presentation is part of the 2019 Magnetic Resonance Velocimetry (MRV) Challenge and represents the combined results from all the participants of the challenge.~ Four research groups have made measurements in the same apparatus comprising a square cross section U-bend with a tight radius that will cause turbulent flow separation.~ An inlet boundary layer trip marks the common coordinate origin of the flow in the channel.~ The apparatus that was transferred between the research labs includes detailed flow conditioning to ensure that variations in supply and exit plumbing will not disrupt the test section flow.~ The test was conducted at a Reynolds Number of 15,000 based on the channel hydraulic diameter, and a tight radius U-Bend ensures a strongly three-dimensional flow field.~ This presentation will focus on the results from each team, which will be compared in the region near the boundary layer trip, at the entrance to and through the U-Bend, and through the exit passageway using velocity field contour plots, iso-surfaces, and quantities derived from the mean velocity components.~ Similarities and differences will be presented which can provide insight into the opportunities that state of the art MRV provides to researchers. [Preview Abstract] |
Sunday, November 24, 2019 9:18AM - 9:31AM |
C07.00007: Investigation of Gas Turbine Cooling Flows Using Magnetic Resonance Velocimetry Wontae Hwang, Seungchan Baek, Sangjoon Lee, Jaehyun Ryu Gas turbine blades are exposed to extreme high temperature, beyond the melting point of the material, thus various methods of advanced cooling are applied. Internal cooling extracts heat from the blade surface via cooling flow within multiple channels inside the blade. These complex channels are spaced tightly together, and it is difficult to perform optical measurements of the flow. To overcome this problem, Magnetic Resonance Velocimetry (MRV) can be utilized to obtain the 3D flow field within these cooling channels. In this study, we demonstrate how we use MRV to analyze the complex flow field within turbine blade cooling structures such as a trailing edge internal channel which has rib turbulators and a thin sharp corner. The data can be used to provide quantitative validation for RANS and LES CFD. [Preview Abstract] |
Sunday, November 24, 2019 9:31AM - 9:44AM |
C07.00008: Phase-Resolved Magnetic Resonance Velocity Measurement for Rotating Turbomachinery Davis Hoffman, Laura Villafane, Christopher Elkins, John Eaton Three-component, time-averaged velocity fields have been measured within a low-speed centrifugal fan with forward curved blades using Magnetic Resonance Velocimetry (MRV). The specific model consists of an impeller with outside diameter of 165 mm inside a hard casing. The design is most suited for automotive HVAC applications. Time-averaged experiments were conducted at Reynolds numbers of 95,700 and 25,000 based on impeller diameter and bulk outlet velocity, yielding three-dimensional mean velocity fields within the entire casing volume. The blade tip speed ratio is maintained at 1.5 in both cases. The mean velocity distribution near the leading and trailing edge of the blades is found to be insensitive to Reynolds number, except where the spacing between the volute wall and the blades is very small. Phase-locked experiments were conducted at the lower Reynolds number to ensure best measurement quality, yielding phase-locked velocity fields between the blades at five positions within a blade passing cycle. Alternating jet-wake structures are observed protruding from each blade passage around the impeller simultaneously. The varying size and shape of separation bubbles on the suction side of the blades is also analyzed as they rotate through an entire revolution. [Preview Abstract] |
Sunday, November 24, 2019 9:44AM - 9:57AM |
C07.00009: Mean Flow Field Measurements in Cavitating Flow Using Magnetic Resonance Velocimetry Supported by X-Ray and Particle Image Velocimetry Kristine John, Martin Bruschewski, Saad Jahangir, Willian Hogendoorn, Evert C. Wagner, Robert F. Mudde, Christian Poelma, Sven Grundmann This presentation focusses on mean flow field measurements in cavitating flow using Magnetic Resonance Velocimetry (MRV). An intrinsic feature of MRV is its ability to measure without optical access. Optical refractions at the phase changes between liquid and vapor phases, which render optical data unusable, do not affect MRV. Moreover, the density of the nuclear spins that is used as a signal source for MRV is typically much higher inside the liquid phase. Void fraction measurements based on signal intensity and measurements of the mean flow velocities in the liquid phase are possible. For a proof-of-concept, flow cavitation in a venturi is investigated. The MRV data is validated with PIV data up to the point of cavitation. For the cavitating cases, X-Ray measurements of the mean void fraction are used as support. It is shown that MRV can provide reliable velocity data. Quantitative void fraction measurements based on the signal intensity of MRV are cumbersome. Flow effects such as turbulence attenuate the signal intensity, which cannot be distinguished from signal voids caused by the vapor phase. The velocity data from MRV must be supported by void fraction data such as from X-Ray. Together, these two techniques provide a valuable tool for studies in cavitating flow. [Preview Abstract] |
Sunday, November 24, 2019 9:57AM - 10:10AM |
C07.00010: Purely Phase-Encoded Magnetic Resonance Mapping of Turbulence Anisotropy Benedict Newling, Amy-Rae Gauthier, Alexander Adair The measurement of flow velocities much greater than 1 m/s can be a challenge for conventional magnetic resonance imaging (MRI) methods. Motion during the spatial encoding interval can lead to a variety of geometric and anemometric distortions. Purely phase-encoded MRI methods, such as SPRITE (single-point ramped imaging with T$_1$ enhancement) can employ a short encoding interval (hundreds of microseconds) for the time-averaged measurement of fast flows. The interval is not only short, but also constant, which saves SPRITE from artefacts caused by interfaces in multi-phase flow. Most recently, we have been using SPRITE to measure mean-squared displacements in turbulent flow in order to quantify the anisotropy of velocity fluctuations. By analogy with diffusion tensor imaging, we measure the components of an eddy self-diffusivity tensor downstream of a Venturi constriction at Reynolds numbers on the order of 10$^5$. [Preview Abstract] |
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